spears live event. First, the massacre at the navy yard, just blocks from the u.S. Capitol. It was the start of the workweek for thousands. As the shooter went on his rampage. So much of the city in lockdown on monday. Even the washington nationals baseball game canceled. And the white house flag at half-staff for the victims. 12 dead plus the gunman. Let's get to what we've learned overnight from jim avila in washington. Good morning, jim. Reporter: Good morning, george. Most of the 15,000 workers here at the massive navy yard have been asked to work from home today, as authorities were on the motive behind this terrible attack, perpetrated by one of the navy's own contractors. This morning, the police are focusing their investigation on 34-year-old aaron alexis, an i.T. Contractor, starting a job at the naval yard. As police and fbi agents searched the home of alexis' parents, authorities gave the all-clear. Allowing more than 1,000 workers stranded all day at the naval facility, to go home. Saying earlier reports of a second and possibly third suspect appear unfounded. We do now feel comfortable that we have the single and sole person responsible. Reporter: The fbi also explaining overnight, how the former sailor could get inside the shipyard. He had clearance. He utilized a valid pass to gain entry to the navy yard. Reporter: It was the beginning of a shooting spree that began at 8:15 in the morning. Police get the first call. Arriving on-scene 15 minutes later. By 8:21, d.C. Metro police and internal navy security begin a series of multiple gun battles. We have an officer down, building 179, on the third floor. Reporter: The shooter uses catwalks on the upper floors in the atrium-style building to shoot down on innocents eating breakfast in the first floor food court. The three shots, were done. Pow, pow, pow. Maybe three seconds later, like four more shots. Reporter: The gunman picking off a dozen victims. None of them in the military. All civilian or navy contractors, suffering fatal gunshot wounds. Many didn't even see him. One of the victims, standing shoulder-to-shoulder, with navy commander tim jirus. I saw him shot in front of me. Reporter: And this morning, we're learning about some of the 1 victims. Ages ranging from 46 to 73. Like 51-year-old arthur daniels. The grandfather of nine was shot in the back as he tried to escape. Or kenneth proctor, the 46-year-old who worked for the government for 22 years. It took nearly 11 hours for authorities to finally clear this huge facility. But frightened workers were hiding in nooks and crannies all over the building. S.W.A.T. Teams finding the last frightened worker hiding in a storage locker at 7:00 last night. Jim, thank you.

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